A single-reviewer hands-on comparison found that Apple Watch Series 12 readings generally tracked a Garmin HRM 600 chest strap during running and indoor cycling, but lagged more and showed occasional irregularities during strength training and HIIT. Apple separately says its study of more than 1,000 people found the Series 12 had the most accurate heart-rate measurement in a wearable.
How the watch and chest strap were compared
The comparison covered more than 100 miles of running, two strength sessions, one bodyweight HIIT workout and one indoor ride. The Apple Watch Series 12 was worn on one wrist; a Garmin HRM 600 chest strap was paired with a Coros Pace 4 Pro to record its readings. The recorded graphs were compared using DC Rainmaker Analyzer.
These were one reviewer’s observations, not a controlled clinical study or a population-wide result.
Running and indoor cycling
During running, readings were generally close once the watch began recording. The comparison also reported brief gaps, occasional dips or spikes, and slower responses to rapid heart-rate changes.
The indoor ride lasted just over 40 minutes and included 30-second sprints every five minutes. The reported average was 109.97 bpm for the Series 12 and 109.89 bpm for the Garmin HRM 600. The watch captured each sprint, with a slight delay at the start of intervals. The near-matching averages and the reported interval lag describe different aspects of that ride: the averages summarize the full session, while the lag occurred as heart rate changed quickly.
Strength training and HIIT
Across two strength sessions, the watch’s readings generally rose and fell with the chest strap, but lagged and rarely aligned exactly. The comparison also reported one small rise that the watch missed; overall average readings were within a couple of beats per minute.
During one five-exercise bodyweight HIIT circuit, which included three jumping exercises, the watch registered the intervals but lagged and produced a couple of erroneous spikes.
| Activity | Apple Watch Series 12 readings versus Garmin HRM 600 | Session details |
| Running | Generally close after readings began; brief gaps, occasional dips or spikes, and slower response to rapid changes | More than 100 miles of running across the comparison |
| Indoor cycling | Averages of 109.97 bpm for the watch and 109.89 bpm for the chest strap; slight lag at interval starts | One ride just over 40 minutes, with 30-second sprints every five minutes |
| Strength training | Readings generally followed the strap but lagged; one small rise was missed | Two sessions; average readings were within a couple of beats per minute overall |
| HIIT | Intervals were captured, with lag and a couple of erroneous spikes | One five-exercise bodyweight circuit, including three jumping exercises |
What the readings mean during a workout
Sampling frequency and accuracy describe different things: sampling frequency is how often a device takes a reading; accuracy is how closely that reading matches a reference. Apple says the Series 12 takes daytime heart-rate measurements every five seconds. Its optical sensor uses green LEDs and light-sensitive photodiodes to detect changes in reflected light associated with blood flow, a method called photoplethysmography. Apple gives the sensor’s stated range as 30–210 beats per minute.
For an electrical heart-rate reading, Apple says to open the Heart Rate app and place a finger on the Digital Crown; in that mode, the watch takes readings every second. Apple also cautions that it cannot guarantee a reliable heart-rate reading for every user at every moment, and that displayed readings can occasionally be abnormally high or low.
